Inserting one's penis rectally, and proceeding to rub the tip of one's phallus around female's lips in a swab-like fashion. Preferably while wearing a thick, goofy, uncoordinated sweater while holding a sandwich, to emphasize the Cosby effect.

The green/brown shade of her upper lips indicated to me she was an expert in the art of the Cosby Swab. She made me drop my hoagie.